Learn how to optimize real-time chat applications for massive scale in this conference talk from Conf42 JS 2024. Explore the architecture of Mattermost and discover key challenges faced when building real-time applications that support 100,000 active users. Dive into practical load testing methodologies, analyze critical client-side performance metrics, and examine concrete examples of performance improvements. Follow along as the speaker shares insights from their experience, starting with architectural fundamentals, progressing through testing strategies, and concluding with actionable optimization techniques that can be applied to large-scale real-time communication systems.